There's a lot of talk about humans living on Mars one day, but radiation levels discovered by NASA's Curiosity rover may spark a new investigation into what is an acceptable amount for people to tolerate over a period of time.

Curiosity, which landed on the Red Planet on August 6, 2012, has been using a tool called a Radiation Assessment Detector to collect radiation samples while on Mars. The goal was to get an idea of how much radiation humans would be exposed to during a round trip to Mars.

Cary Zeitlin, NASA's principal scientist for the Martian Radiation Environment Experiment, found (through Curiosity) that humans could be exposed to between 554 and 770 millisieverts of ionizing radiation. This largely depends on the level of solar activity.

Americans typically receive about 6.2 millisieverts a year from both natural and man-made sources.

What does this mean, exactly? Zeitlin isn't entirely sure; as his team just makes measurements and doesn't decide what radiation dose is considered safe. The amount of radiation found falls in line with what was expected in a "deep space radiation environment," but as far as health goes, more information is needed.

Astronauts traveling to the moon receive about the same rate of radiation accumulation as those traveling to Mars, but since the Mars trip is so much longer than the moon's (the Apollo moon mission took about 8 days while the Curiosity Mars mission took about 253 days) the radiation levels may be more dangerous.

Zeitlin mentioned that there's no effective method of shielding that could block all of the high-energy particles from reaching the astronauts on a Mars mission.

There are also some studies that say radiation exposure is linked to cancer, and NASA tries to keep its lifetime fatal cancer risk to 3 percent for its astronauts.

NASA released a report in 2010 that said the average 35-year-old American male can safely spend between 140 and 186 days in deep space with heavy shielding while a 35-year-old female could spend between 88 and 120 days. For those who have never smoked, the 35-year-old man could spend between 180 and 239 days in deep space while a 35-year-old female could spend between 130 and 173 days. These figures keep them below the 3 percent cancer risk.

Zeitlin said the radiation astronauts would receive on a Mars trip would be comparable to getting an abdominal CT scan once every five days.